U.S. patent number 4,250,424 [Application Number 05/946,018] was granted by the patent office on 1981-02-10 for rotor of synchronous machines.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Kunio Miyashita, Hiroshi Sento, Tadao Shimozu, Shoji Tanabe, Seiji Yamashita.
United States Patent |
4,250,424 |
Sento , et al. |
February 10, 1981 |
Rotor of synchronous machines
Abstract
The rotor core of a synchronous motor or a synchronous generator
with a permanent magnet is comprised of a multiplicity of laminated
thin iron sheets each having as many segments as the poles. Slits
are formed between each adjacent segment, and the magnetic
reluctance of the slits is made larger than that between the rotor
core and the stator core, thereby minimizing the leakage fluxes
within the rotor core. Each segment is required to be prevented
from being broken away by centrifugal force generated while the
machine is in operation. According to the invention, adjacent
segments are connected by a non-magnetic material through the
slits. The non-magnetic material is fitted in the recesses formed
at both sides of the slit in such a manner as to connect them with
each other, each of the recesses being positioned substantially
parallel to the circumference of the rotor and having a wider
bottom than the opening thereof.
Inventors: |
Sento; Hiroshi (Sakura,
JP), Tanabe; Shoji (Sakura, JP), Shimozu;
Tadao (Sakura, JP), Yamashita; Seiji (Katsuta,
JP), Miyashita; Kunio (Hitachi, JP) |
Assignee: |
Hitachi, Ltd.
(JP)
|
Family
ID: |
11493952 |
Appl.
No.: |
05/946,018 |
Filed: |
September 26, 1978 |
Foreign Application Priority Data
|
|
|
|
|
Jan 11, 1978 [JP] |
|
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53/1170 |
|
Current U.S.
Class: |
310/216.133;
310/216.004; 310/216.116; 310/256; 310/265; 310/43 |
Current CPC
Class: |
H02K
21/46 (20130101); H02K 1/276 (20130101) |
Current International
Class: |
H02K
1/27 (20060101); H02K 21/00 (20060101); H02K
21/46 (20060101); H02K 001/22 () |
Field of
Search: |
;310/195,183,197,181,182,162,163,211,217,156,261,216,264,265,42 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Skudy; R.
Attorney, Agent or Firm: Craig & Antonelli
Claims
We claim:
1. A rotor of synchronous machines comprising:
a rotor core including a multiplicity of laminations of blanked
iron sheets each having segments divided by a plurality of slits,
said segments corresponding in number to the number of poles, each
of said blanked iron sheets having a center hole, and said
laminations being made in such a manner that said holes and said
slits of all of said blanked iron sheets are arranged in alignment
at the same positions;
a plurality of permanent magnets which are received by said center
holes of said blanked iron sheets so as to provide each pole
constituted by said segments of said blanked iron sheets with a
specific polarity;
a rotary shaft arranged in said center holes concentrically with
said rotor core and adapted to rotate integrally with said rotor
core and said permanent magnets;
a plurality of recesses formed in both sides of each of said slits
and having a bottom wider than the opening; and
a plurality of key members with the ends thereof securely fitted
with said recesses across said slits respectively.
2. A rotor of synchronous machines according to claim 1, in which
said key members are made of a nonmagnetic material.
3. A rotor of synchronous machines according to claim 1, in which
said laminations of said blanked iron sheets each with adjacent
segments connected by a plurality of bridges magnetically saturated
with a small amount of magnetic flux make up said rotor core.
4. A rotor of synchronous machines according to claim 1, in which
each of said key members includes part of non-magnetic material
crossing each of said slits and parts of magnetic material
integrated with said part of non-magnetic material and inserted
into said recesses.
5. A rotor of synchronous machines comprising:
a rotor core including a multiplicity of laminations of blanked
iron sheets each having segments divided by a plurality of slits,
said segments corresponding in number to the number of poles, each
of said blanked iron sheets having a center hole, and said
laminations being made in such a manner that said holes and said
slits of all of said blanked iron sheets are arranged in alignment
at the same positions;
a plurality of permanent magnets which are received by said center
holes of said blanked iron sheets so as to provide each pole
constituted by said segments of said blanked iron sheets with a
specific polarity;
a rotary shaft arranged in said center holes concentrically with
said rotor core and adapted to rotate integrally with said rotor
core and said permanent magnets;
a plurality of recesses formed in both sides of each of said slits
and having a bottom wider than the opening;
a plurality of flattened sleeves each with the ends thereof
inserted into each of said recesses across each of said slits;
and
a plurality of pins each inserted in the part of each of said
sleeves positioned within each of said recesses so as to anchor
said sleeves fast to said recesses.
6. A rotor of bipolar synchronous machines comprising:
a rotor core including a multiplicity of laminations of blanked
iron sheets each having two segments divided by two slits, each of
said blanked iron sheets having a center hole, and said laminations
being made in such a manner that said holes and said slits of all
of said blanked iron sheets are arranged in alignment at the same
positions;
a plurality of permanent magnets which are received by said center
holes of said blanked iron sheets so as to provide one pole
constituted by one of said segments of each of said blanked iron
sheets with the polarity N and the other pole constituted by the
other of said segments of each of said blanked iron sheets with the
polarity S;
a rotary shaft arranged in said center holes concentrically with
said rotor core and adapted to rotate integrally with said rotor
core and said permanent magnets;
a plurality of recesses formed in both sides of each of said slits
and having a bottom wider than the opening; and
a plurality of key members with the ends thereof securely fitted
into said recesses across said slits respectively.
Description
BACKGROUND OF THE INVENTION
This invention relates to a rotor of synchronous machines, and in
particular to a reinforcement of the rotor against the centrifugal
force generated in synchronous machines rotating at high speed.
The rotor core of a synchronous machine is comprised of a
multiplicity of laminations of blanked iron sheets. In many cases,
the blanked iron sheets have as many segments and bridging sections
connecting the segments as the poles. Between adjacent segments,
slits extending from a point near the inner periphery to a point
near the outer periphery are provided, so that the magnetic
reluctance between adjacent segments is made larger than that
between the rotor core and the stator core. In other words, the
slits are provided for the purpose of minimizing the leakage
magnetic fluxes within the rotor core. The bridging sections are
provided in order to facilitate the assembly of segments, which
would be difficult in the absence of the bridging sections on the
one hand, and to absorb the centrifugal force while the machine is
in operation on the other hand. The bridging sections, however, are
required to be easily magnetically saturated and therefore are
limited in width. Thus the mere provision of the bridging sections
is not sufficient if the segments are to remain coupled strongly to
each other against the centrifugal force.
As a measure against the centrifugal force, the method disclosed in
Japanese Patent Kokai (Laid-Open) No. 3170/71 is well known.
According to such a method, a clamp of non-magnetic material is
provided over different segments on the outer periphery of the
rotor, and both ends of the clamp, together with damper windings,
are inserted fixedly into the slots, thereby coupling the segments
to each other securely. In this configuration, the clamp has a
uniform thickness and the ends thereof are only bonded between the
slot and the damper winding. Further, in view of the difference in
the coefficient of thermal expansion between the rotor core
material and the damper winding material, a temperature change may
cause a gap between the slot and the damper winding. The resulting
disadvantage is a reduced ability of the clamp to couple the
segments, thereby leading to a lower resistance to the centrifugal
force. The undesirable gap between the slot and the damper winding
inevitably develops especially due to the fact that the temperature
of the rotor in operation is about 100.degree. C. higher than that
of the rotor in stationary state. If a clamp with high rigidity is
used, the clamp with the ends thereof bent at right angles and
inserted into the slots is capable of enduring a considerable
centrifugal force. However, a higher rigidity requires a
considerably large thickness of the clamp.
If the thickness of the clamp is increased, the space between the
stator core and the rotor core is required to be enlarged
accordingly. As a result, the machine portion with the clamp has an
increased magnetic reluctance, so that when the machine is operated
as a motor, the AC magnetic field in acceleration cannot enter the
rotor easily at the clamp. Thus a greater starting current is
required and the accelerating torque is reduced. Furthermore, when
the machine is operated as a generator, the output voltage contains
more high harmonics. In order to minimize these disadvantages, the
thickness of the clamp is limited, resulting in an unsatisfactory
measure against the centrifugal force.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
rotor of synchronous machines which is sufficiently high in
resistance to the centrifugal force.
Another object of the present invention is to provide a rotor of
synchronous machines which are capable of being operated with a
small starting current and satisfactory accelerating torque.
Still another object of the invention is to provide a rotor of
synchronous machines which are capable of being operated as a
generator with an output voltage containing a small amount of high
harmonics.
The above and other objects, features and advantages will be made
apparent by the detailed description taken in conjunction with the
accompanying drawings.
According to the present invention, there is provided a rotor core
comprising a multiplicity of laminations of blanked iron sheets.
Each of the blanked iron sheets has segments in the same number as
the poles and is divided by the slits extending from a point near
the inner periphery towards the outer periphery. Corresponding to
each segment is provided a permanent magnet of a specific polarity.
The rotor core and the permanent magnets are adapted to rotate
integrally with the rotary shaft. From the viewpoint of ease of
assembly and endurance against centrifugal force, the segments are
preferably connected by bridge sections which cross the slits and
are easily saturated magnetically. The slits may extend either
radially of the rotary shaft of the rotor core or somewhat spirally
from the inner peripheral side towards the outer periphery. The
slits may also take such a form as to extend toward the outer
periphery, somewhat return towards the inner periphery, and again
extend towards the outer periphery. Each of the slits may have
uniform width or may have a wider part for accommodating the
permanent magnet. Recesses opened in the direction substantially
parallel to the circumference are formed at both sides of the
slits. The recesses have a bottom wider than the opening thereof
for the purpose of securely fitting a key member into the recesses
across the slit. This key member is preferably made of a
non-magnetic material, but may be comprised of a magnetic material
if the material and size thereof are so selected that it is
magnetically saturated by a small amount of magnetic fluxes. As
another alternative, the key member may comprise a non-magnetic
material with a wedge-shaped magnetic material welded to the sides
thereof in such a manner that the part thereof crossing the slit
consists of the non-magnetic material. The last-mentioned
construction facilitates the passage of magnetic flux even through
the recesses, thereby advantageously making uniform the magnetic
flux density over the whole segments. As still another alternative,
a flattened sleeve may be inserted into the recesses so that into
those parts of the sleeve positioned in the recesses, pins are
driven and thus the particular parts of the sleeve are enlarged,
with the result that the sleeve and the pins make up a key member,
thus facilitating the insertion of the key member into the
recesses. The number of the key members crossing each slit and the
number of the recesses for receiving the ends of the key member may
be determined by the required strength. The space other than
occupied by the key member in the slits may be filled with such a
non-magnetic material as aluminum, so that the key member is hard
to move in the slit and therefore is strengthened.
According to the above-mentioned construction of the present
invention, the centrifugal force exerted on the rotor core is
absorbed into the key member. Also, in view of the fact that the
key member is securely fitted in the recess with a bottom wider
than the opening thereof, the segments are strongly coupled to each
other and thus prevented from being separated from each other even
under a considerably large centrifugal force.
Furthermore, the key member is located inwardly of the outer
periphery of the rotor core where the magnetic characteristics are
hardly affected, thus making it possible to provide a uniform air
gap between the rotor core and the stator core over the entire
periphery. The result is only a small starting current is required
and sufficient accelerating torque is provided when the machine is
operated as a motor, while an output voltage with few high
harmonics is obtained when the machine is operated as a generator.
In addition, the present invention is applicable to a machine
without any damper winding like the generator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a section in a plane perpendicular to
the axis of a two-pole rotor of a synchronous machine according to
an embodiment of the present invention.
FIG. 2 is a sectional view taken along the line II--II in FIG.
1.
FIGS. 3 and 4 are diagrams showing part of a section in a plane
perpendicular to the axis of the rotor of a synchronous machine
according to other embodiments of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1 and 2, reference numeral 1 shows blanked iron sheets
each having segments in the same number as the poles. In the
embodiment shown, the machine has two poles and therefore each
sheet has two segments 2, 3. Between the segments 2 and 3, two
slits 6 and 7 extending from a point near the inner periphery 4
towards the outer periphery 5 are formed. Generally, the two
segments 2 and 3 are connected integrally by bridges 8, 9, 10 and
11. The width of the bridges 8, 9, 10 and 11 is sufficiently large
to prevent the segments 2 and 3 from being separated from each
other before being assembled for the purpose of facilitating the
assembly work, but sufficiently narrow to facilitate magnetic
saturation for the purpose of minimizing the leakage of magnetic
flux between the segments. The blanked iron sheets 1 have a
multiplicity of slots 12 in the neighbourhood of the periphery
thereof and a center hole 13 at the central part thereof. The
blanked iron sheet 1 has the slits 6 and 7 which in turn have
recesses 14, 15, 16 and 17 formed at both sides substantially
parallel to the circumference of the iron sheet. Each of the
recesses 14, 15, 16 and 17 has a bottom wider than the opening
thereof. A multiplicity of the blanked iron sheets with such a
construction are laminated in such a manner that the center holes
13, the slots 12, the slits 6 and 7, and the recesses 14, 15, 16
and 17 of all the sheets are arranged in registration at the same
positions respectively, thus making up a rotor core 18. Across the
slits 6 and 7, key members 19 and 20 of non-magnetic materials such
as stainless steel are mounted with the ends thereof securely
fitted into the recesses 14, 15, 16 and 17 respectively. A rotary
shaft 21 is arranged in the center hole 13 concentrically with the
rotor core 18. A boss 22 with a rectangular section is fitted over
the rotary shaft 21 in such a manner prohibiting relative motion
thereof with the rotary shaft. Permanent magnets 23 and 24 are
inserted between the opposed sides of the boss 22 and the rotor
core 18 respectively. The two permanent magnets 23 and 24 are
arranged in such a manner as to be connected in the direction
perpendicular to the longitudinal direction of the slits 6 and 7.
The permanent magnet 23 is arranged with the N pole thereof
directed outward and the permanent magnet 24 with the S pole
thereof directed outward; In other words, the segment 2 exhibits
the polarity N and the segment 3 the polarity S the segments being
of magnetic material as parts of blanked iron sheets 1. Support
discs 25 and 26 are provided to hold the rotor core 18 at the
longitudinal sides thereof. The support discs 25 and 26 are
securely fitted on the rotary shaft 21 and, through the step 27
formed on the rotary shaft 21 and the fastening nut 28, press the
rotor core 18 inwardly from both sides thereof. The support disc 26
is fitted before the boss 22 on the rotary shaft 21. The fastening
nut 28 is screwed on the thread 29 cut on the rotary shaft 21.
Conductors 31 are formed in the slots 12 by die casting. A
squirrel-cage winding is comprised of conductors 31 cast in the
slots 12, and end rings 32 and 33 for electrically connecting all
the conductors 31 on both sides of the rotor core 18. The
squirrel-cage winding 30 may be caused to act as a starting winding
when the rotor is used as a motor; and to act as damper winding
after the rotor has been started. The squirrel-cage winding 30
fails to function and therefore the slots 12 are not required when
the rotor is used as a generator.
The key member 20 shown in FIG. 3 is comprised of a non-magnetic
material 20a such as stainless steel on both sides of which
magnetic materials 20b and 20c are welded at points 34
substantially parallel with the circumference of the iron sheet. In
other words, the part 20a of the key member 20 which crosses the
slit 7 is made of stainless steel, and the parts 20b and 20c
thereof inserted into the recesses 16 and 17 of iron.
In the embodiment shown in FIG. 4, the ends of the sleeve 20d of
non-magnetic material in the form of a flattened cylinder are
inserted into the recesses 16 and 17 across the slit 7, and then
the pins 20e and 20f of magnetic material are pressed into the
sleeve 20d in the recesses 16 and 17. The recesses 16 and 17 shown
in FIGS. 3 and 4 are substantially circular, and the slots 12 shown
in FIG. 4 are of the enclosed type.
In each of the above-mentioned embodiments, the space in the slits
6 and 7 remaining after the key members 19 and 20 are pressed in
are filled with aluminum 35.
* * * * *